Which channels & band is better

Dear bro

Now i installed RB3011 & WAP AC for 400feet room…but all wifi device rx signal around -56 to -80…i think i setup got problem…

second question is how to know which channels at my home is the best…

thank you bro

Well, the range of -80…-56 isn’t bad at all. I tend to say that -80 is the lower limit but -56 is surely great, probably even a bit too high.
You can check the frequency utilization with the “Frequency Usage” button in WinBox’’ wireless interface window (you need to do it on the AP directly, it’s not (yet) supported in CAPsMAN in case you’re using that).
Or by terminal with

/interface wireless frequency-monitor wlan2

Good luck
-Chris